1. Field of the Invention
The present invention relates to a liquid ejection method, a liquid ejection apparatus, a double-side printing method, and an image recording apparatus for double-side printing. In particular, the present invention relates to technology for preventing floating of mist and thereby preventing contamination caused by two liquids being mixed, in an inkjet apparatus which uses the two-liquid type of ink. Moreover, the present invention also relates to technology for carrying out double-side printing while it prevents contamination on a head due to floating mist occurring during ejection of liquid in an inkjet apparatus which uses a two-liquid type of ink.
2. Description of the Related Art
In the related art, as an image forming apparatus, an inkjet printer (inkjet recording apparatus) is known, which includes an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (liquid ejection ports) and which records images on recording medium by ejecting ink (liquid) from the nozzles toward the recording medium while it causes the inkjet head and the recording medium to move relatively to each other.
An inkjet head of an inkjet printer includes pressure generating units. For example, each pressure generating unit includes: a pressure chamber to which ink is supplied from an ink tank via an ink supply channel; a piezoelectric element which is driven by an electrical signal in accordance with image data; a diaphragm which constitutes a portion of the pressure chamber and deforms in accordance with the driving of the piezoelectric element; and a nozzle which is connected to the pressure chamber. The volume of the pressure chamber is reduced in accordance with the deformation of the piezoelectric element, and the ink inside the pressure chamber is thereby ejected from the nozzle in the form of a droplet. An image is formed on a recording medium by combining dots formed by ink droplets ejected from the nozzles of the pressure generating units.
In an inkjet printer of this kind, when ink is ejected from each nozzle of the inkjet head, not only intended ink droplets for forming the image but also very small ink droplets are ejected from the nozzles. Moreover, a portion of an ink droplet rebounds when the droplet is deposited on the recording medium, and it floats in the form of a very small ink droplet. Ink mist thus occurs in the space between the inkjet head and the recording medium.
In cases where an inkjet printer comprising inkjet heads which respectively eject colored inks and forming color images, the ink mist discharged from one inkjet head deposits onto the nozzle surface of another inkjet head, and contamination (hereinafter, this kind of contamination is simply referred to as “contamination between heads”) thus occurs. Moreover, there is a possibility that the correct operation of the apparatus is obstructed because of the deposition of the ink mist onto the interior of the apparatus.
Inkjet-type image forming apparatuses are known in which radiation-curable ink, such as an ultraviolet-curable ink (so-called UV ink), is used and droplets of the radiation-curable ink deposited on a recording medium are exposed to radiation in order to cure the ink droplets rapidly, whereby image quality is improved and the recording speed is increased. For example, in a two-liquid type of inkjet head, a treatment liquid containing an ultraviolet curing initiator and an ink containing the base curing material (polymerizable compound) are ejected from different heads. In this case, if contamination on the nozzle surfaces occurs between the head for ejecting the treatment liquid and the head for ejecting the ink (the nozzle surface of the head for the treatment liquid or the nozzle surface of the head for the ink is contaminated by a mist generated from the other head), then the ink solidifies on the nozzle surface and the nozzles become blocked, and ejection defects may thus arise.
The main factor for the occurrence of contamination of this kind is the fact that mist generated during the ejection is moved by the airflow due to the conveyance of the recording medium and the mist is deposited onto the nozzle surfaces of heads positioned further downstream. Therefore, in the related art, in order to prevent contamination of this kind, the distance between heads is increased, the airflow is suppressed by reducing the conveyance speed of the recording medium, or maintenance of the heads is carried out frequently.
Furthermore, in the related art, the attempts mentioned below have been made to recover the ink mist actively.
For example, Japanese Patent Application Publication No. 2004-330637 discloses a recording apparatus which records images on a recording medium by ejecting ink droplets from nozzles of a recording head that moves in a direction perpendicular to the conveyance direction of the recording medium. In this recording apparatus, mist recovery devices are arranged on both ends with respect to the movement (scanning) of the recording head. The mist recovery device (upstream mist recovery device) disposed on the upstream side of the recording head in terms of the scanning direction suctions air, whereas the other mist recovery device (downstream mist recovery device) expels air.
Moreover, for example, Japanese Patent Application Publication No. 2004-330446 discloses a recording apparatus including a flow regulator mechanism having a deflection surface. The flow regulator mechanism is arranged on the downstream of the head surface in terms of the relative movement direction in which the head member is relatively moved with respect to the recording medium by a scanning device. The deflection surface is provided with an absorbing member for absorbing liquid mist. The deflection surface smoothly deflects the airflow so as not to affect the speed of the airflow generated over the head surface due to the relative movement of the head member caused by the scanning device.
Furthermore, for example, Japanese Patent Application Publication No. 2003-11334 discloses an inkjet recording apparatus which uses ink containing an ultraviolet curing agent and records onto a recording medium while it performs reciprocating movement of a recording head in a main scanning direction. In this inkjet recording apparatus, when ink is ejected while the recording head is moved, ultraviolet light is radiated onto the ink deposited on the recording medium, from a position in front of the ink ejection unit in terms of the movement direction of the recording head.
Moreover, various inkjet recording apparatuses with an inkjet head for carrying out double-side printing onto a recording medium have been proposed in the related art.
For example, Japanese Patent Application Publication No. 2003-266802 discloses an inkjet recording apparatus in which a first printing unit and a second printing unit are disposed in mutually opposing positions. The first printing unit and the second printing unit respectively print onto a first side face and a second side face of a recording medium, in a simultaneous fashion.
Moreover, for example, Japanese Patent Application Publication No. 2005-88207 discloses an inkjet recording apparatus including a paper inverting device. In this inkjet recording apparatus, after printing on the front surface of a recording paper, the recording paper is once conveyed to the paper inverting device and is inverted. The recording paper is then returned to the conveyance device, and printing is carried out onto the rear surface of the recording paper. Double-side printing is carried out in this way. Moreover, this inkjet recording apparatus uses ink which is subjected to an aggregation reaction, in order to prevent bleeding and print-through, and the like, of the ink deposited on the paper, which may be problematic especially in the case of double-side printing.
Furthermore, for example, Japanese Patent Application Publication No. 2005-67051 discloses an inkjet recording apparatus for double-side printing. In this inkjet recording apparatus, an image is formed on one surface of a recording medium, and a portion of the recording medium is then outputted to a paper output tray. The recording medium is then drawn back into the main body of the inkjet recording apparatus, and the recording medium is conveyed and sent to a double-side conveyance path by a switch-back system. Double-side printing is carried out in this way.
However, in the technology described in Japanese Patent Application Publication No. 2004-330637, in order to prevent contamination between the heads by recovering the mists generated by the heads, it is necessary to dispose a mist recovery device for each of the heads. The spaces for the mist recovery devices hence need to be provided, and therefore, the recording apparatus becomes large in size. Moreover, when the distance between the heads is increased, displacement of the dot positions is liable to occur; therefore, it becomes difficult to achieve high image quality. Furthermore, in order to achieve high image quality, highly precise conveyance is necessary, and accordingly the costs can be increased.
Similarly, in the technology described in Japanese Patent Application Publication No. 2004-330446, if it is sought to prevent contamination between the heads by recovering the mists of the heads, then it is necessary to dispose a flow regulating mechanism between the heads, and consequently apparatus size can be increased, image quality may be reduced, and costs can be increased.
In the technology described in Japanese Patent Application Publication No. 2003-11334, it is necessary to dispose ultraviolet light radiation units on either side of the head, and therefore space for this installation is required. Moreover, in order to prevent the ink from curing on the ejection surface due to the effects of the ultraviolet light, it is necessary to increase the distance between the ultraviolet irradiation unit and the heads. Therefore, apparatus size can be increased.
Thus, in each of the related art cases described above, there are obstacles, such as increased size of the apparatus, degradation of image quality due to increase in the distance between the heads, and increased costs as a result of the need for high-precision conveyance. The related art technologies described above relate to a shuttle type head in which a recording head is moved in a direction perpendicular to the conveyance direction of the recording medium. However, in a line-type of semi-fixed head, since depositing position errors become more readily recognizable in comparison with a shuttle type of head, then the effects of contamination are very marked. If it is sought to avoid this kind of situation by means of frequent maintenance, then it is necessary to move a wiping blade or a cap to the underside (maintenance position) of the semi-fixed head and to implement maintenance. This maintenance action requires time and labor, and moreover, the productivity declines due to the increase in the frequency of maintenance.
In a case where liquids (reaction-liquids) of a two-liquid reaction type are ejected, it is difficult to remove the liquids that are hardened due to the curing reaction caused by contamination between the two liquids even if the maintenance action is performed, and moreover, ejection failures may arise due to curing in the nozzle units. In the related art method which recovers ink mist as described above, it is difficult to prevent contamination between heads sufficiently.
In the technology described in Japanese Patent Application Publication No. 2003-266802, since heads (print units) are disposed so as to face each other, then liquid droplets and ink mist discharged from one head are liable to be deposited onto the nozzle surface of the other head. Therefore, contamination can occur between the heads, leading to deterioration of the image. In particular, in cases of using reactive ink, contamination on the nozzle surface of the head occurs and the ink becomes cured, leading to blocking of the nozzles.
In the technology described in Japanese Patent Application Publication No. 2005-88207, the ink head unit Y and the ink head unit K, which respectively eject Y ink and K ink reacting with the Y ink, are disposed in mutually adjacent positions as shown in FIG. 14 in Japanese Patent Application Publication No. 2005-88207. Therefore, there is a possibility that Y ink mist deposits onto the nozzle surface of the head K, because of the airflow created by the conveyance of the paper. If the Y ink mist deposits onto the nozzle surface of the head K, then an aggregation reaction occurs between the Y ink and the K ink, thus leading to the occurrence of nozzle blockages, which are the cause of image deterioration. Moreover, as shown in FIG. 1 in Japanese Patent Application Publication No. 2005-88207, since the inverting mechanism projects to the outer side of the head rows, then the installation surface area of the apparatus is increased. In addition, surplus space is also required for a cover, or the like, which is provided in the conveyance path in order to prevent the adherence of dirt, and the like, to the surface of the printed medium.
In the technology described in Japanese Patent Application Publication No. 2005-67051, similarly to the technology described in Japanese Patent Application Publication No. 2005-88207, there is a possibility that the installation surface area of the apparatus increases since a switch-back unit is provided on the outer side of the apparatus. Moreover, the technology described in Japanese Patent Application Publication No. 2005-67051 does not take account of the occurrence of contamination between the heads.